The correct answer is option 'D' - A and B only.

Taxes on railway freights and fares, stamp duties on financial documents, and tolls are all examples of union taxes. However, taxes on railway freights and fares and stamp duties on financial documents are specifically mentioned as union taxes in the Indian Constitution, while tolls are not.

Here is a detailed explanation of why option 'D' is the correct answer:

1. Taxes on railway freights and fares:
- This refers to the taxes levied on the transportation of goods and passengers by railways.
- The power to levy and collect taxes on railway freights and fares is exclusively vested with the Union Government, as mentioned in Article 269 of the Indian Constitution.
- These taxes are collected by the Union Government and contribute to the central revenue.

2. Stamp duties on financial documents:
- Stamp duty is a tax levied on various financial documents like agreements, bonds, share certificates, debentures, etc.
- The power to levy and collect stamp duties on financial documents is vested with the Union Government, as mentioned in Article 246 of the Indian Constitution.
- Stamp duties are collected by the Union Government and shared with the states based on the provisions of the Indian Stamp Act.

3. Tolls:
- Tolls refer to the charges collected for the use of roads, bridges, highways, or other transportation infrastructure.
- While tolls are a form of revenue generation for the government, they are not specifically mentioned as union taxes in the Indian Constitution.
- Tolls can be levied and collected by both the Union Government and state governments, depending on the ownership and jurisdiction of the infrastructure.

In summary, taxes on railway freights and fares and stamp duties on financial documents are mentioned as union taxes in the Indian Constitution, while tolls are not. Therefore, option 'D' - A and B only - is the correct answer as it includes tolls, which are not categorized as union taxes.

Option C should be the correct answer.